1. Field of the Invention
The present invention relates to a tire vulcanizing press and a split die device for vulcanizing tires mounted to vehicles.
2. Description of Related Art
In vulcanizing a tire, a heating medium of high temperature and high pressure (steam, steam plus inert gas, or warm water) is admitted into the inside of a tire, so that the die tends to be opened by the pressure of the heating medium. Since crude rubber is softened by the increase in temperature, in the event of opening of die, not only does the tire being vulcanized becomes defective, but also the heating medium blows off through the tire. For this reason, the tire vulcanizing machine is so constructed that the die is incorporated in the crank press or liquid pressure press to prevent the die from opening by pressing the die during vulcanization of tire. Therefore, the main frame or other structures must withstand this pressing force, which makes the machine heavy and expensive.
An example of a conventional tire vulcanizing machine will be briefly explained with reference to FIGS. 10 through 12. In these figures, right and left of line G--G, H--H, and I--I indicate the cases where the die thickness is different. Reference numeral 101 denotes a main frame, which can vulcanize two tires at the same time. Reference numeral 102 denotes a container incorporating a die split into a plurality of parts, 103 denotes a bolster plate which attaches to the die and raises and lowers it, 104 denotes an upper center mechanism incorporating a tire centering mechanism, 3 denotes a lower center mechanism including a bladder operating mechanism and a passage for admitting a tire inside heating medium into the bladder, 105 denotes a die thickness adjusting cap connected to the upper center mechanism with screws, 106 denotes a pressurizing cylinder, 107 denotes rails for moving the pressurizing cylinder when the die is opened to set or remove a tire, 108 denotes a liquid pressure cylinder for raising and lowering the bolster plate 103, 8 denotes a loader for loading a crude tire, and 9 denotes an unloader for unloading the vulcanized tire. Even for vulcanizing passenger car tires, the pressurizing cylinder must deliver an output of about 130 tons per tire. Therefore, the main frame 101, the upper center mechanism 104, and other members must withstand this output.
As another type of machine, the technology in which upper and lower clamp domes 45, 46 are connected and released by a lock ring 48 has been proposed as disclosed in Japanese Patent Laid-Open No.132306/1991. With this technology, the upper and lower clamp domes 45, 46, the lock ring 48, and other members must withstand the above-described pressing force, which requires a high cost. In vulcanizing a tire, a heating medium of high pressure (for example, 25 kg/cm.sup.2) is admitted into the inside of a crude tire (into the molding bladder 2 in Japanese Patent Laid-Open No.132306/1991) after the die is closed. Therefore, the upper and lower side dies tend to be opened by the inside pressure reaction. For the tread die, the radial inside pressure reaction changes the direction of force on the slope of an outer ring, so that the outer ring tends to open in the same direction as that of the side dies. Therefore, the die must be closed by overcoming the resultant force of these inside pressure reactions. For this purpose, the presses disclosed in FIG. 10 and Japanese Patent Laid-Open No.132306/1991 are equipped with a die clamping mechanism having a strength greater than the inside pressure reaction on the press body side.
The tire vulcanizing machine shown in FIGS. 10 through 12 has a guide bracket installed at each side of bolster plate for attaching the die and transmitting the die clamping force, a square rail installed inside a portal frame disposed at each side of the bolster plate, and a plurality of rollers installed so as to grip the square rail from three directions (the rollers are incorporated into the guide bracket). The rollers can be adjusted in relation to the square rail by means of an eccentric bushing which can make adjustment so that the gap is zero or a pre-load is given in the entire process in which the bolster plate is raised and lowered. Near the circular peripheral end of the bolster plate, the rod end of the elevating cylinder disposed diagonally is connected, and the cylinder is mounted at an appropriate place at the upper part of the frame. With such a die opening/closing mechanism, the bolster plate can be vertically guided exactly along the square rail by means of the elevating cylinder, and the bolster plate can be raised or lowered while being kept horizontal against the imbalance of the thrust of the elevating cylinder.
However, the tire vulcanizing machine shown in FIGS. 10 through 12 has the following problems:
(1) The adjustment of rollers using the eccentric bushing requires high technique. PA1 (2) The adjusting work must be done regularly after the initial adjustment. PA1 (3) Even if the elevating cylinders are manufactured with high accuracy, a difference in cylinder output is produced after long-term operation by the internal leakage or the relative difference in piston packing resistance due to aging, producing an inclination or vibration of the bolster plate. PA1 (1) Because the elevating cylinders are located at positions far apart from the center of die. PA1 (2) A vulcanizing press requires an apparatus for loading a crude tire and that for unloading a finished tire. For the arrangement and installation of these apparatuses, Japanese Utility Model Laid-Open No.127409/1990 is not suitable. The reason for this is as follows: Because the frame of the opening/closing guide is positioned outside the press, PA1 (1) Although the tread molding die is changeable, a segment for attaching the die, a guide for opening/closing the segment, and an opening/closing drive mechanism are integral parts of structure of the vulcanizing press. Therefore, the tread molding die can be changed only on the press, so that the operation for production must be stopped during the die change; efficient die change cannot be performed. PA1 (2) The upper and lower side dies must be changed independently. PA1 (3) Since the die is heated usually to a temperature as high as 150.degree. C. or higher in use, the work for changing the die in the press is dangerous. Accordingly, the work efficiency is decreased. PA1 (4) Since the replacement die is cold, it must be heated to the temperature in use after troublesome and inefficient change work. Therefore, the machine cannot be used for several hours after the die change. When a wide variety of tires of different sizes and patterns are produced, the frequency of die change becomes high, which decreases the productivity, whereby the producer suffers a serious disadvantage. PA1 (1) To this end, the tire vulcanizing press of the present invention uses a split die device having an upper disk to which an upper die portion for molding the tire side is attached, a lower disk to which a lower die portion for molding the tire side is attached, divided segments to which a split tread die portion for molding the tire tread is attached, and an outer ring which has an inner inclined surface corresponding to the outer inclined surface of the segment and are slidably engaged with the outer inclined surface. Each of the divided segments has protrusions at the upper part and the lower part, so that the protrusions engage with the outer peripheries of the upper and lower disks to lock the upper and lower disks to prevent the disks from separating when the die is closed. When the die is opened and the segments move outward, the locking condition is released, by which the upper die portion and the lower die portion are separated to receive a crude tire. After the die is closed, the separating action of upper and lower disks generated when a pressurized heating medium is admitted into the inside of the tire is inhibited by the segments, whereby the transmission of internal reaction to the press body is minimized. PA1 (2) The outer ring is fixed to a bolster plate which is in a fixed relation to a center mechanism operating cylinder, the segments are supported by the upper disk which is in a fixed relation to a piston rod of the center mechanism operating cylinder in such a manner as to slide horizontally. PA1 (3) A column for attaching guide rails for opening/closing the die is disposed at the intermediate portion between the right and left dies. This column is also used as a column for the guide rails for the crude tire loading apparatus and the finished tire unloading apparatus. PA1 (4) The column at the intermediate portion is of a T shape when viewed from the front, and elevating cylinders are disposed at positions slightly offset from the die center to the guide bracket side, preferably near the center of gravity of the entirety of the guide bracket and the elevating plate. PA1 (5) When a pressurized heating medium is admitted into the inside of tire after the die is closed, the divided segment is subjected to internal pressure reaction in the radial outward direction. This internal pressure reaction is converted into a vertical reaction by the slope effect of an annular body of the split die device (though the reaction is lessened by friction), which tends to raise the elevating disk and the annular body. To resist this tendency, a downward force is always produced on the elevating cylinder. With the hydraulic upright-type press, the elevating cylinders for opening/closing the die is in a free condition during vulcanization. PA1 (6) In the case of (5), the die opens if the elevating cylinder or the circuit fails, which is undesirable. As an alternative or a second safety measure, a split die opening/closing operation cylinder is used. That is, the cylinder disposed at the die center portion is mounted to the bolster plate, and the rod side is connected to the upper disk of the split die device. This split die opening/closing operation cylinder is operated in the direction in which the rod is pulled up during vulcanization, so that the upper disk and the bolster plate are pulled, by which the die closing condition is kept. PA1 (7) As another alternative of (5) and (6), a mechanism for preventing the die from opening, which engages with the groove on the annular body side of the split die device, is installed at the lower base of the press. PA1 (8) As another method of (7), a mechanism for preventing the die from opening, which engages with the rod of the split die operation cylinder when die is closed, is installed at the bolster plate portion. PA1 (1) The forces which to tend to open the die, which are produced by the action of pressurized heating medium admitted into the inside of tire via a bladder, are balanced in the split die device. PA1 (2) As a result of (1), a pressurizing cylinder of high pressure and high output which was required in the conventional machine can be omitted. PA1 (3) Since the pressure reaction acting on the main frame is eliminated, the weight of the main frame can be significantly reduced, and the construction of the main frame can be simplified. PA1 (4) The die can be changed by the same procedure as that of the conventional multi-split die. PA1 (5) The need for the device for adjusting the die thickness can be eliminated.
By using the device disclosed in Japanese Utility Model Laid-Open No.127409/1990, that is, a straight track bearing commercially available as a finished product, the work for adjusting the roller gap may be lessened, and the problem of inclination or vibration of bolster plate due to the difference in output of the elevating cylinder may be solved.
However, the device in Japanese Utility Model Laid-Open No.127409/1990 has the following problems:
(a) The guide bracket must be rigid since it is subjected to a moment due to a shaping reaction (molding reaction in pre-expansion) acting at the die center as a resultant force in the process in which the die is closed. PA2 (b) A moment due to bonding force between the tire and the die acting at the die center as a resultant force occurs in the direction opposite to the moment of (a) in the process in which the die is opened. This also requires high rigidity of the guide bracket. PA2 (c) The press should be operated as fast as possible from the viewpoint of productivity; while a low speed is required in the process of pre-molding and the process in which the tread die is opened, that is, the process in which the tire tread is separated from the tread die. In this speed change from high to low speed and in a sudden stop for emergency to prevent an accident, a very high inertia force is produced near the die center because a position near the die center is the center of gravity, by which a moment is produced at the guide bracket. PA2 (a) The tire loading apparatus and the tire unloading apparatus must be separated at right and left, that is, they must be near the frame. This runs counter to the aim of providing an economical press which is operated with right and left simultaneous operation cycle. PA2 (b) If the tire loading apparatus and the tire unloading apparatus are positioned at the center of right and left dies to solve the problem of (a), a rigid column is needed for the tire loading apparatus and the tire unloading apparatus in addition to the frame. This also runs counter to the aim of providing an economical machine. PA2 (c) Since the frame is positioned outside, an auxiliary means, for example, to connect both frame columns at the top to increase the rigidity of the guide frame is needed. This is objectionable in pursuing economy.
When the device disclosed in Japanese Utility Model Laid-Open No.127409/1990 is used practically, therefore, the guide bracket must be considerably rigid, and a considerably large straight track bearing must be used; an economical opening/closing mechanism cannot be provided.
Although the conventional vulcanizing machine described above is so constructed that any of a split die and a vertically two-piece die which are known in the industry can be used, almost all machines have recently used the split die because the demand for higher quality and performance of the radial ply tire has increased. Regarding a vulcanizing press using a split die only, U.S. Pat. No. 4,871,305 has been known.
However, this U.S. Patent has the following problems:
To solve the above problems, many producers are exerting their ingenuity for fast changing of split die device and quick start-up of production by changing the die including the opening/closing mechanism (every split die device usually called a sectional mold container) which has been preheated, while strongly demanding the automation of die attaching/detaching work to a press. For this reason, the vulcanizing press of U.S. Pat. No. 4,871,305 cannot be said to be suitable for efficient die change.